P eracarida — Mysidacea , Cumacea. 
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The eyes, when present, are stalked and movable. There are Table- 
swimming branches (exopodites) on the thoracic legs. 
Most of the Mysidacea live in the sea and many species are 
found on the British coasts. Macromysis flexuosus is one of the 
commonest species. A coloured drawing of the closely allied 
Leptomysis is hung in Wall- case No. 5. A drawing of Arachno- 
mysis leuckarti in the Table-case gives an example of the remark- 
able forms assumed by some deep-sea members of the Order. The 
family Lophogastridae, all of which are inhabitants of the deep 
sea, reach a much greater size than do the members of the other 
families. A specimen of Gnathophausia calcardta from the 
“ Challenger ” expedition is exhibited, and alongside of it is placed 
Gnathophausia willemoesii, female, from the side, one-half natural size. 
gr., a groove dividing the last abdominal somite. (From Lankester’s 
“ Treatise on Zoology,” after Sars.) 
a copy of a coloured drawing from a living specimen of G. wil- 
lemoesii (Big. 19), showing the vivid red coloration characteristic 
of many deep-sea Crustacea. 
Order 2.— Cumacea. 
A carapace is present, but it leaves four or five of the pos- 
terior thoracic somites free. The eyes are not stalked, and are 
usually coalesced into one. Swimming branches (exopodites) are 
usually present on some of the thoracic limbs. The abdomen is 
generally very slender, and the last pair of appendages (uropods) 
are elongated. The other abdominal appendages are absent, at 
least in the female. 
The Cumacea are all marine, burrowing in sand and mud, and 
being occasionally taken in great numbers swimming at the 
surface of inshore waters. As a rule, they are very small, the 
specimens of the common British species Iphinoe trispinosa here 
